Vibrational Raman Spectra from the Self-Consistent Charge Density Functional Tight Binding Method via Classical Time-Correlation Functions

The Self-Consistent Charge Density Functional Tight Binding (SCC-DFTB) method has been extended for the calculation of vibrational Raman spectra employing the Fourier Transform of Time-Correlation Function (FTTCF) formalism. As Witek and co-workers have already shown for a set of various organic molecules, the minimal basis SCC-DFTB approach performs surprisingly good in terms of polarizability calculations. Therefore, we were encouraged to use this electronic structure method for the purpose of Raman spectra calculations via FTTCF. The molecular polarizability was accessed via second order numeric derivatives of the SCC-DFTB energy with respect to the components of an external electric field “on-the-fly” during a molecular dynamics (MD) simulation. The finite electric field approach delivers Raman spectra that are in overall good agreement for most of 10 small organic model compounds examined in the gas phase compared to a standard Normal Mode Analysis (NMA) approach at the same (SCC-DFTB) and at a highe...